It is well known in the arts that aluminum oxide ceramics may be prepared in relatively low cost and have excellent properties, particularly, in terms of mechanical strength and heat resistance. Accordingly, aluminum oxide has been widely used for in various applications.
As one of the practical applications of the aluminum oxide for mechanical purposes, a part in a machine required having highly wear resistance, for example, materials for tools, sliding parts, etc., has been sintered. However, since the requirements for each application have become more severe, materials capable of attaining higher performance are further demanded. In particular, the materials having high wear resistance are desired.
To comply with such requirements, attempts have been made to improve in wear resistance by adding various carbides into the aluminum oxide.
Materials made of aluminum oxide in which various carbides are simply added generally show large crystal grains, and not satisfy the above-noted severe requirements since the dislodgement of grains from the sintered material is liable to be caused when such material is subjected to abrasion. Therefore, these materials cannot be accepted as having sufficient wear resistance.
Also, aluminum oxide materials containing carbides has drawbacks in that if the carbide is present in an amount of less than 5 wt %, the material shows insufficient wear resistance; on the other hand, the more the amount of carbides is present, the lower the mechanical strength, depending on the carbides, becomes.
The reason for the above phenomenon is not clear so far; however, it is considered to be related to the fact that interfacial bonding between the aluminum oxide grains and various carbides grains is weak, and that the aluminum oxide grains are not sufficiently pulverized.
For instances, JP-A-62-59567 (a term "JP-A" used herein means unexamined Japanese patent publication) discloses a ceramic material having excellent wear resistance which principally comprises 5 to 20 weight % of titanium carbide and the rest of alumina. Since the titanium carbide, per se, is added as one of the starting materials, the effect according to the present invention in terms of the wear resistance cannot be attained.
JP-A-52-104515 and JP-A-63-129061 disclose preparation of alumina/titanium carbide ceramic material in which titanium carbide is formed by chemical reaction in a firing step; however, no third component, which is required as an indispensable component to fulfill the objects according to the present invention, is present in the composition. Accordingly, the product obtained by the chemical reaction step in these references cannot form pulverized grain of the present invention.